Recent advances in combustion technology have employed the use of high velocity gas injection into a combustion zone to carry out combustion with reduced nitrogen oxides (NO.sub.x) generation. Nozzles with relatively small diameters are employed in order to achieve the high velocities. The high gas velocities cause furnace gases to be aspirated or entrained into the high velocity gas which has a dampening effect on NO.sub.x generation.
A problem with high velocity gas injection into a combustion zone is that the furnace gases, which may comprise particulate matter and condensible vapors, cause the nozzles, which have small openings to begin with, to foul or corrode easily as the furnace gases are aspirated or entrained into the high velocity gas exiting the nozzle. The furnace gases also tend to be quite hot, on the order of 1000.degree. F. or more, which exacerbates the fouling and corrosion problem.
One way of dealing with this problem has been to provide a large amount of water cooling to the nozzle so as to prevent high temperature corrosion or melting. However, a water cooling system is complex to operate and does not address the fouling problem where the furnace atmosphere has a high particulate content. Moreover, water cooling can escalate the corrosion and fouling problems when the furnace atmosphere contains condensible vapors.
Ceramic nozzles have been proposed as a solution to the fouling problem in high velocity gas injection. However, presently available ceramic nozzles are not suitable for industrial scale operations because of corrosion and cracking due to thermal and other stresses.
It is desirable therefore to have a high velocity gas injection system which will enable one to carry out combustion in a combustion zone without generating a high level of NO.sub.x while reducing the fouling experienced with presently available systems.
Accordingly it is an object of this invention to provide a method for injecting high velocity gas into a combustion zone while avoiding the high level of nozzle fouling experienced with the use of presently available methods.
It is another object of this invention to provide a high velocity gas injection apparatus which can inject high velocity gas into a combustion zone without extensive nozzle fouling.